1. Field of the Invention
The present invention relates to a method of equipment for control of the fuel and air to be supplied to an internal combustion engine with a fuel-reforming device.
2. Description of the Prior Art
For the purpose of reducing the harmful emission from a spark ignition internal combustion engine, a "lean" combustion of fuel is desirable. For this "lean" combustion, a fuel containing molecular hydrogen is useful.
There are conventionally two methods of supplying hydrogen to an internal combustion engine. In one method, hydrogen is carried on a vehicle in a high pressure vessel or in the form of, for example, liquified hydrogen or metal hydride. In the other method, mainly liquid hydrocarbon is reformed on the vehicle to yield a hydrogen-containing gas to be delivered to the engine. Of these two methods, the latter is preferable on account of its greater safety and availability for the existing fuel supply system.
The air excess rate of the engine which has a direct bearing on harmful emission and the fuel consumption depends upon the method selected for reforming hydrocarbon to yield a hydrogen-containing gas. The so-called partial oxidation method in which the air and hydrocarbon are reacted at an extremely low ratio of air to fuel in the presence of a catalyst is most popularly adopted on vehicles. In the vehicle-mounted fuel-reforming device based on the partial oxidation method, a complicated electronic control method or a rough method utilizing a small carburetor has been used for exact control of the air/fuel ratio in the fuel-reforming device or the air excess rate in the internal combustion engine.
Under application of the conventional electronic method of control, the equipment can be mechanically simplified but, electrically, it is considerably complicated, necessitating feedback control of the air flow rate or accurate setting of time lag and other factors. Meanwhile, under mechanical control utilizing, for example, a carburetor, exact control of the engine in all its operational ranges is very difficult, resulting in a lessening of the desirable effect of using the fuel-reforming device. Further, these two methods involve the difficulty of resetting the conditions when the displacement or compression ratio of the engine changes.
In the case of a gasoline-burning engine, the gas can be reformed in the permissible range of air/fuel ratios in the fuel-reforming device of 1.5 to 6, the range being adaptable up to the maximum of 4 times of flow rate fluctuations.
In the case of an internal combustion engine, however, the range in which combustion can take place with little yield of harmful emission is relatively narrow, that is, it is limited to 1.2-1.6 in terms of the air excess rate, which means that the maximum allowable range of flow rate fluctuations is a mere 30%. Thus, the fuel-reforming device tolerates a relatively rough control, while the internal combustion engine calls for an exact control.
Under application of the electronic control, the gas reforming conditions or the engine burning conditions can be controlled with considerably high accuracy. However, this is more than necessary and, is rather undesirable, because the combustion control of the engine is sacrificed for the control of the fuel-reforming device. Mechanical control by the carburetor, however, is not favorable for the internal combustion engine which needs exact control, because the fuel volume depends on the air volume supplied to the fuel-reforming device. Accordingly, the fluctuation of the air volume to the fuel-reforming device directly affects the burning state in the engine.